1. Field of the Invention
This invention relates to a reel driving apparatus for a miniature video camera in which a tape frequently needs to be instantaneously advanced backward reversed during its forward advance.
2. Description of the Prior Art
The prior reel driving apparatus for a miniature video camera is of the type shown in FIGS. 1 and 2 of the accompanying drawings, in which a drive unit functioning to wind and unwind a tape (not shown) extending between a feed reel and a take-up reel comprises, as shown in FIG. 1, a belt pulley (2) rotated by a belt(1) transmitting power from a motor (not shown) to the pulley, and an idle gear(3) being in intermeshing engagement with a gear of the belt pulley (2) to be rotated thereby. The belt pulley and the idle gear are mounted on a single support plate(4) which is pivotally movable about a center shaft(5) of the belt pulley (2) between a feed reel gear(6) and a take-up reel rear(7), which gears are disposed each on the opposite sides of the center shaft.
With this arrangement, when the support plate(4) is rotated in a counter-clockwise direction as viewed in FIG. 1 so that the idle gear (3) mounted thereon is engaged with the feed reel gear (6), the tape feed reel may be rotated via a gear train comprising the gear of the belt pulley(2), the idle gear(3) and the feed reel gear(6), thereby unwinding the tape therefrom.
Conversely, when the support plate(4) is rotated in a clockwise direction, the take-up reel may be rotated via a gear train comprising the gear of the belt pulley (2), the idle gear(3) and the take-up reel gear(7), thereby winding the tape thereon.
In addition, in contrast to a common video cassette recorder, the miniature video camera is provided with a rotary gear assembly (9) comprising a direction rotating gear(8) disposed in intermeshing engagement with the take-up reel gear(7) so as to control the rotation of the take-up reel depending upon a rotational direction of the take-up reel gear(7). In the miniature video camera, the reason for controlling the rotation of the take-up reel by means of the rotary gear assembly is as follows. Generally, the miniature video camera repeatedly carries out picture-taking and stop operations for the purpose of its use. Every time the camera is operated, the tape needs to be repeatedly advanced forward and reversed depending upon various modes of the operation.
Therefore, in the course of such forward advances and reverses of the tape, especially when the forward advancing tape is temporarily stopped, thereafter is slightly moved backward and remains in the pause condition according to a change of the operation from a picture recording mode to a temporary stop or pause mode, because the inertia force disappears and then acts again on the tape, the tape is not unwound uniformly from the take-up reel. In such case, the amount of the tape being wound again on the feed reel is not as great as the amount of tape excessively unwound from the take-up reel due to temporary over-rotation of the take-up reel. In order to prevent the slackening of the tape, therefore, an attempt has been made to apply tension to the tape on the take-up reel by controlling the rotation of the reel.
The construction and operation of the rotary gear assembly functioning to prevent the tape from slackening due to the temporary over-rotation of the take-up reel as discussed above will now be described in more detail below.
As shown in FIG. 2, the rotary gear assembly(9) having the one-way rotating gear(8) held in intermeshing engagement with the take-up reel gear(7) comprises three tapered rectangular holes(10) formed in the rotary gear assembly in circumferentially spaced relation to each other, cylindrical bearings (11) received one in each of the taper holes (10) and a compression spring (12) disposed in each one of the taper holes(10) to apply its biasing force to each one of bearings(11). With this construction, in the picture recording mode and a play mode of the video camera, in which the idle gear (3) is engaged with the take-up reel gear(7), as the take-up reel gear is rotated in a clockwise direction, the bearings (11) are moved to and positioned at the wide portions of the taper holes(10). Thus, the one-way rotating gear(8) may be rotated without interference, and therefore the take-up reel gear(7) may be rotated smoothly. In this condition, when the mode of the operation is changed to a review mode in which the tape is reversed, or the pause mode in which the tape must be slightly reversed the idle gear (3) is engaged with the feed reel gear (6) to rotate the feed reel in a counter-clockwise direction, and thus the take-up reel (14) is rotated in a counter-clockwise direction through a cassette tube (not shown). At this point, because the one-way rotating gear(8) of the rotary gear assembly (9) has a tendency to rotate in a clockwise direction contrary to the counter-clockwise rotation of the take-up reel, the bearings (11) are moved to the narrow portions of the taper holes (10), thereby impeding the rotation of the one-way rotating gear(8).
Consequently, the take-up reel gear(7) engaged with the rotating gear(8) is also prevented from rotating, and only the take-up reel(14) is rotated while being subjected to frictional force by a friction clutch (13) disposed between the take-up reel(14) and the take-up reel gear(7). As a result, the take-up reel tightens the tape wound thereon, thereby preventing the tape from slackening. This prior apparatus is however disadvantageous in that the rotary gear assembly is complex in construction and requires a large number of parts, resulting in increasing the manufacturing cost and weight of a product.